CN110831285A

CN110831285A - Constant current source load driving device and lighting lamp

Info

Publication number: CN110831285A
Application number: CN201911237576.9A
Authority: CN
Inventors: 许瑞清; 刘立国
Original assignee: Beijing Mould Electric Semiconductor Co Ltd
Current assignee: Beijing Mould Electric Semiconductor Co Ltd
Priority date: 2019-12-06
Filing date: 2019-12-06
Publication date: 2020-02-21
Anticipated expiration: 2039-12-06
Also published as: CN110831285B

Abstract

The invention discloses a constant current source load driving device, which comprises a power conversion stage, a controller integrated circuit and a power supply resistor. The constant current source load driving device has the overcurrent protection function of the power switch, so that the power switch is comprehensively protected, and the reliability of a circuit is improved. In addition, the constant current source load driving device does not increase the circuit cost, and has obvious market advantages under the condition of extremely high competition of the LED illumination market.

Description

Constant current source load driving device and lighting lamp

Technical Field

The invention relates to a constant current source load driving device, in particular to a constant current source load driving device with a power switch overcurrent protection function and an illumination lamp comprising the driving device.

Background

As a new generation of illumination light sources, Light Emitting Diodes (LEDs) have been widely used. In the global lighting market, LED lighting is expected to account for seven, eight or more decades. Over the years, LED constant current controllers and driving devices have been evolving. The circuit structure of the latest LED load driving device in the market at present is shown in fig. 1. In the driving device, the constant current controller chip 300 can be produced by adopting a common process design, so that the cost is low; and the peripheral elements are fewer, and the overall performance is superior to that of the traditional circuit structure. However, this drive device has a problem in that the power switch 307 is not overcurrent-protected, which means that the power switch 307 runs the risk of accidental overcurrent burnout.

Disclosure of Invention

The invention aims to provide a new constant current source load driving mechanism aiming at the problems of the LED load driving device in the prior art on the premise of not increasing the circuit cost, so that the power switch is effectively protected from overcurrent.

According to a first aspect of the present invention, there is provided a constant current source load driving apparatus, comprising a power conversion stage, a controller integrated circuit and a supply resistor, wherein the power conversion stage comprises a power switch, an inductor charge/discharge current detection resistor, a freewheeling diode and a capacitor; the drain electrode of the power switch is connected with an input voltage source, and the source electrode of the power switch is connected to a node between an inductor and the reference ground of the controller integrated circuit through an inductor charging/discharging current detection resistor; the other end of the inductor is connected with the anode of the fly-wheel diode; the negative electrode of the freewheeling diode is connected with a VCC node between the power supply resistor and one end of the capacitor; the other end of the capacitor is connected to a node between the source electrode of the power switch and the inductance charging/discharging current detection resistor and is used as a filter capacitor of the constant current source load; the controller integrated circuit provides overcurrent protection for the power switch based on an inductive charge/discharge current detection signal from the power conversion stage; and, on the basis of shielding the inductance charging current detection signal from the inductance charging/discharging current detection signal, determining the average output current of the constant current source load.

Preferably, a constant current error circuit, an overcurrent protection circuit and a driver are arranged in the controller integrated circuit, wherein the constant current error circuit shields the inductor charging current detection signal for the inductor charging/discharging current detection signal according to a driving signal output by the driver; and performing integral averaging on the inductor discharge current detection signal to generate an amplified error signal; the overcurrent protection circuit receives the amplified error signal and the inductive charging/discharging current detection signal to generate a PWM signal; the input end of the driver receives the PWM signal, and the output end of the driver is connected with the grid electrode of the power switch.

Preferably, the constant current error circuit comprises a first NMOS transistor, a second NMOS transistor, a phase inverter and an error amplifying circuit, wherein the drain of the first NMOS transistor is connected to an input terminal of the error amplifying circuit, the source of the first NMOS transistor is connected to the reference ground of the controller integrated circuit, and the gate of the first NMOS transistor receives the driving signal output by the driver; the drain electrode of the second NMOS tube receives the inductive charging/discharging current detection signal, the source electrode of the second NMOS tube is connected with the input end of the error amplification circuit, and the grid electrode of the second NMOS tube receives the driving signal through the phase inverter; the other input end of the error amplifying circuit is connected with a first reference voltage, and the output end of the error amplifying circuit generates an amplified error signal.

Preferably, the constant current error circuit comprises a shielding resistor, an NMOS transistor and an error amplifying circuit, wherein one end of the shielding resistor is connected to the inductive charge/discharge current detection signal, and the other end of the shielding resistor is connected to a node between a drain of the NMOS transistor and an input end of the error amplifying circuit; the source electrode of the NMOS tube is connected with the reference ground of the controller integrated circuit, and the grid electrode of the NMOS tube receives the driving signal output by the driver; the other input end of the error amplifying circuit is connected with a first reference voltage, and the output end of the error amplifying circuit generates an amplified error signal.

Preferably, the resistance of the shielding resistor is more than 100 times smaller than the resistance of the integrating resistor in the error amplifying circuit and more than 100 times larger than the resistance of the inductor charge/discharge current detection resistor.

Preferably, the overcurrent protection circuit comprises a peak comparator, a current-limiting comparator, a valley comparator, an and gate circuit and a trigger, wherein one input end of the peak comparator receives the amplified error signal, the other input end of the peak comparator receives the inductance charging/discharging current detection signal, and the output end of the peak comparator is connected with one input end of the and gate circuit; one input end of the current-limiting comparator receives the inductance charging/discharging current detection signal, the other input end of the current-limiting comparator is connected with a second reference voltage, and the output end of the current-limiting comparator is connected with the other input end of the AND circuit; one input end of the valley comparator receives the inductance charging/discharging current detection signal, the other input end of the valley comparator is connected with a third reference voltage, and the output end of the valley comparator is connected with the reset end of the trigger; and the setting end of the trigger is connected with the output end of the AND gate circuit, and the output end of the trigger generates the PWM signal.

Preferably, the third reference voltage is at or near zero volts.

Preferably, the second reference voltage is 3 times or more than 3 times the first reference voltage.

According to a second aspect, there is provided a lighting fixture comprising the driving apparatus of the first aspect and an LED load.

According to the invention, the constant current source load driving device has the overcurrent protection function of the power switch, so that the comprehensive protection of the power switch is realized, and the reliability of the circuit is improved. And importantly, the constant current source load driving device does not increase the circuit cost, and under the condition that the market competition of the LED illumination is extremely severe, the constant current source load driving device has obvious market advantages, which is the value of the constant current source load driving device.

Drawings

For a better understanding of the present invention, the following examples are provided to further illustrate the present invention in conjunction with the accompanying drawings. In the drawings:

fig. 1 is a circuit structure diagram of a recent LED load driving apparatus in the current market;

FIG. 2 is a cost-increasing LED load driving device modification;

fig. 3 is a graph comparing the voltage at the resistor 501 and the resistor 306 with the inductor current waveform in fig. 2;

fig. 4 is a circuit configuration diagram of a constant current source load driving apparatus according to an embodiment of the present invention;

FIG. 5 is an example of the constant current error circuit 670 of FIG. 4;

fig. 6 is another example of the constant current error circuit 670 of fig. 4;

fig. 7 is an example of the overcurrent protection circuit 560 in fig. 4.

Detailed Description

To solve the problem of providing overcurrent protection for the power switch, the most conceivable solution is to directly connect a current-limiting resistor 501 in series between the source of the power switch 307 and the reference ground ICGND of the controller chip 500, for detecting the magnitude of the current flowing through the power switch 307, as shown in fig. 2. The greater the current flowing through the power switch 307, the greater the voltage across the current limiting resistor 501. When the voltage reaches the upper limit, the overcurrent protection is triggered, and the controller chip 500 immediately turns off the power switch 307, so as to realize the overcurrent protection.

The solution shown in fig. 2 is completely feasible in theory, but has two disadvantages, namely, an additional peripheral component resistor 501 and an additional pin of the controller chip 500. The former increases the cost and is a major contradiction. The cost of one resistor is about 1 RMB, the monthly demand of the LED constant current controller reaches hundreds of millions, and the loss caused by more than one resistor is very considerable. It can be seen that adding current limiting resistor 501 is not cost effective.

The inventor considers that, in this scheme, the current limiting resistor 501 and the constant current resistor 306 (for setting the load current) are both connected to the reference ground ICGND of the controller chip 500, and there is a possibility that these two resistors are combined. The inventors have carefully examined the behavior of these two resistors. The switching power supply is characterized in that the power switch only works in a fully-ON (ON) state or a fully-OFF (OFF) state, and a third state does not exist. At the stage of turning on the power switch 307, the terminal voltage VIN on the rectifying and filtering capacitor 102 charges the inductor 309 through the power switch 307, the charging current linearly increases from a small current, and the current generates a proportional voltage signal through the current limiting resistor 501, and the proportional voltage signal is sent to the controller chip 500 for overcurrent protection judgment; at this time, the freewheeling diode 308 is in reverse turn-off, so no current flows through the constant current resistor 306 (the current flowing through the power supply resistor 103 is lower than 200uA, the resistance of the constant current resistor 306 is only a few ohms, and the voltage drop generated by this current is less than 1 mv, so it is negligible), and the terminal voltage across the constant current resistor 306 is zero. In the stage of turning off the power switch 307, no current flows through the current-limiting resistor 501, and the end voltage on the current-limiting resistor 501 is zero; at this time, the inductor 309 is in the discharging stage, the inductor current passes through the freewheeling diode 308 to the VCC node, then flows to the CS node through the capacitor 604 and the LED load 111, and finally flows through the constant current resistor 306 to return to the inductor 309, and the terminal voltage on the constant current resistor 306 is proportional to the inductor discharging current at this stage.

Referring to fig. 3, fig. 3 is a graph showing a relationship between the terminal voltages of the current limiting resistor 501 and the constant current resistor 306 and the inductor current waveform. It can be seen that the terminal voltage waveforms of the current limiting resistor 501 and the constant current resistor 306 are exactly complementary, the current limiting resistor 501 only detects the charging current of the inductor, and the constant current resistor 306 only detects the discharging current of the inductor, which provides a favorable condition for combining the two resistors.

Referring to fig. 4, fig. 4 is a circuit structure diagram of a constant current source load driving device according to an embodiment of the present invention. In this driving apparatus, the current limiting resistor and the constant current resistor are combined into an inductor charge/discharge current detection resistor 606 that can detect both the inductor charge current flowing through the power switch 307 and the inductor discharge current.

As shown in fig. 4, the driving apparatus includes a power conversion stage, a controller integrated circuit 600, and a supply resistor 103. The power conversion stage is composed of a power switch 307, an inductor 309, an inductor charge/discharge current detection resistor 606, a freewheeling diode 308 and a capacitor 604. The drain of the power switch 307 is connected to the input voltage source VIN, and the source thereof is connected to the node between the inductor 309 and the controller integrated circuit reference ground ICGND through the inductor charge/discharge current detection resistor 606; the other end of the inductor 309 is connected with the anode of the freewheeling diode 308; the negative electrode of the freewheeling diode 308 is connected to the VCC node between the supply resistor 103 and one end of the capacitor 604; the other end of the capacitor 604 is connected to a node between the source of the power switch 307 and the inductor charge/discharge current detection resistor 606, and serves as a filter capacitor for the LED load 111.

The controller integrated circuit 600 provides overcurrent protection to the power switch 307 based on the inductive charge/discharge current sense signal CS from the power conversion stage. Specifically, during the charging phase of the inductor 309, the power switch 307 is turned on, the freewheeling diode 308 is turned off in the reverse direction, and the charging current flows through the detection resistor 606; this current increases linearly from the valley value, and when the terminal voltage of the detection resistor 606 (i.e., the signal CS) reaches the threshold of the over-current protection, the over-current protection will be triggered immediately and the power switch 307 will be turned off immediately, preventing the power switch from being burned out. And, the controller integrated circuit 600 determines the average output current of the LED load 111 on the basis of masking the inductor charge/discharge current detection signal CS from the inductor charge current detection signal.

Inside the controller integrated circuit 600, sub-circuit modules such as the power management circuit 150, the constant current error circuit 670, the overcurrent protection circuit 560, and the driver 180 may be provided. The power management circuit 150 is used to detect whether the operating voltage (i.e., the VCC node voltage) of the controller integrated circuit 600 is within a normal range, and to provide appropriate voltages and currents for other sub-circuit modules within the integrated circuit 600. The constant current error circuit 670 shields the inductor charging current detection signal CS from the inductor charging/discharging current detection signal CS according to the driving signal DRV output from the driver 180; and performs integral averaging on the inductor discharge current detection signal to generate an amplified error signal EAOUT. The over-current protection circuit 560 receives the amplified error signal EAOUT and the inductive charge/discharge current detection signal CS to generate a PWM signal. The driver 180 has an input terminal receiving the PWM signal and an output terminal connected to the gate of the power switch 307.

In the driving apparatus, the inductor charging/discharging current detection signal CS sent to the constant current error circuit 670 includes both an inductor charging current detection signal and an inductor discharging current detection signal, and the constant current error circuit 670 only needs the inductor discharging current detection signal, so the circuit needs to shield the inductor-off charging current detection signal.

Referring to fig. 5, fig. 5 is an example of the constant current error circuit 670 of fig. 4. The constant current error circuit 670 includes

NMOS transistors

676, 775, an inverter 677, and an error amplification circuit. The error amplifier circuit is composed of an error amplifier 371, an integrating resistor 372, and an integrating capacitor 373. As shown in fig. 5, the drain of the NMOS transistor 676 is connected to an input terminal CSEA of the error amplifier circuit, the source is connected to the ground reference ICGND of the controller integrated circuit 600, and the gate receives the driving signal DRV output by the driver 180; the drain of the NMOS 775 receives the inductor charge/discharge current detection signal CS, the source is connected to the input CSEA of the error amplifier circuit, and the gate receives the driving signal DRV through the inverter 677; the other input terminal of the error amplifying circuit is connected to the reference voltage VREF1, and the output terminal generates an amplified error signal EAOUT.

In this example, only useful inductor discharge current detection signals are sent to the error amplification circuit for integral averaging. When the driving signal DRV is high, the inductor 309 starts to charge, the NMOS tube 676 in the constant current error circuit 670 is completely turned on, and the CSEA node is pulled to zero level; meanwhile, the NMOS 775 is in a closed state, so that the external inductor charge/discharge current detection signal CS is not affected by the DRV signal. And the input level received by the error amplifying circuit is zero. When the driving signal DRV is low, the inductor 309 starts to discharge, at this time, the NMOS transistor 676 is completely turned off, the NMOS transistor 775 is completely turned on, and the external signal CS is directly sent to the error amplifying circuit. Therefore, the error amplification circuit only performs integral averaging on the inductive discharge current detection signal, and the average output current of the LED load 111 is determined by the following formula:

I_LED＝VREF1/R₆₀₆(1)

fig. 6 is another example of the constant current error circuit 670 of fig. 4. As shown in fig. 6, the constant current error circuit 670 may alternatively include a screening resistor 675, an NMOS transistor 676, and an error amplifier circuit. Similarly, the error amplifier circuit is composed of an error amplifier 371, an integrating resistor 372, and an integrating capacitor 373. One end of the shielding resistor 675 is connected with an inductive charging/discharging current detection signal CS, and the other end of the shielding resistor 675 is connected with a node CSEA between the drain electrode of the NMOS tube 676 and one input end of the error amplifying circuit; the source electrode of the NMOS tube 676 is connected with the reference ground ICGND of the controller integrated circuit 600, and the gate electrode receives the driving signal DRV output by the driver 180; the other input terminal of the error amplifying circuit is connected to the reference voltage VREF1, and the output terminal generates an amplified error signal EAOUT.

Similarly, when the driving signal DRV is high, the inductor 309 starts to charge, the NMOS transistor 676 inside the constant current error circuit 670 is fully turned on, pulling the CSEA node to zero, so that the input level received by the error amplifier circuit is zero. Here, it is preferable that the resistance of the shielding resistor 675 is more than 100 times larger than the resistance of the inductive charge/discharge current detecting resistor 606, but the resistance of the shielding resistor 675 is more than 100 times smaller than the resistance of the integrating resistor 372 in the error amplifying circuit. When the driving signal DRV is low, the inductor 309 starts to discharge, the NMOS transistor 676 is completely turned off, and the external inductor charge/discharge current detection signal CS is directly sent to the error amplifying circuit. In this way, the error amplification circuit can also integrate and average only the inductor discharge current detection signal, and the average output current of the LED load 111 is still determined by the above equation 1.

Referring to fig. 7, fig. 7 is an example of the overcurrent protection circuit 560 in fig. 4. In this example, the over-current protection circuit 560 includes a peak comparator 563, a current limit comparator 561, a valley comparator 564, an and circuit 562, and a flip-flop 565. One input end of the peak comparator 563 receives the amplified error signal EAOUT from the constant current error circuit 670, the other input end receives the inductor charging/discharging current detection signal CS, and the output end is connected to one input end of the and circuit 562; one input end of the current-limiting comparator 561 receives the inductor charging/discharging current detection signal CS, the other input end is connected to the reference voltage VREF2, and the output end is connected to the other input end of the and circuit 562; the valley comparator 564 has an input terminal receiving the inductor charge/discharge current detection signal CS, another input terminal connected to the reference voltage VREF3, and an output terminal connected to the reset terminal R of the flip-flop 565; the set terminal S of the flip-flop 565 is connected to the output terminal of the and circuit 562, and the output terminal generates a PWM signal, which is supplied to the driver 180.

Under the normal condition that no overcurrent occurs, as long as the voltage of the inductance charging/discharging current detection signal CS exceeds the output signal EAOUT of the constant current error circuit, the output of the peak value comparator 563 is changed from high level to low level; at this time, the output of the current-limiting comparator 561 is still high (at this time, EAOUT < VREF2, so the output of the current-limiting comparator 561 is also high), so that the and circuit 562 outputs a low level to set the flip-flop 565 following it, so that the PWM signal changes from high to low, and the power switch 307 is turned off.

Under the conditions of overcurrent caused by various accidents such as peripheral device faults, controller chip defects and the like, the voltage of an inductor charging/discharging current detection signal CS is greater than a current limiting reference voltage VREF2, and a current limiting comparator 561 can immediately output a low level signal OCP (over current protection); the OCP signal is logically anded with the output of peak comparator 563 (when EAOUT > VREF2, so that the output of peak comparator 563 is high), and a low signal is generated to set flip-flop 565, so that the PWM signal changes from high to low, immediately turning off power switch 307, thereby implementing an overcurrent protection function. Preferably, the reference voltage VREF2 may be 3 times or more than 3 times the reference voltage VREF1 in the constant current error circuit. For example, the reference voltage VREF1 may be 200mV and the reference voltage VREF2 may be 600 mV.

The reset signal of flip-flop 565 is provided by valley comparator 564. After the power switch 307 is turned off, the inductor 309 enters a discharging stage, and the CS voltage at two ends of the inductor charging/discharging current detection resistor 606 linearly decreases; when the CS voltage is lower than the reference voltage VREF3, the valley comparator 564 will output a high signal to reset the flip-flop 565, so that the PWM signal goes from low to high, turning on the power switch 307 again. Thus, self-excited switching oscillation is formed in a cycle. Here, the reference voltage VREF3 is preferably at or near zero volts, e.g., 10 mV.

In the foregoing description, although the present invention is exemplified to drive an LED load, it is easily understood by those skilled in the art that the present invention can be used to drive any kind of constant current source load.

It will be apparent that there are many variations of the invention described herein which are not to be regarded as a departure from the spirit and scope of the invention. Accordingly, all such modifications as would be obvious to one skilled in the art are intended to be included within the scope of this invention as set forth in the following claims.

Claims

1. A constant current source load driving device comprises a power conversion stage, a controller integrated circuit and a supply resistor, wherein,

the power conversion stage comprises a power switch, an inductor charging/discharging current detection resistor, a freewheeling diode and a capacitor; the drain electrode of the power switch is connected with an input voltage source, and the source electrode of the power switch is connected to a node between an inductor and the reference ground of the controller integrated circuit through an inductor charging/discharging current detection resistor; the other end of the inductor is connected with the anode of the fly-wheel diode; the negative electrode of the freewheeling diode is connected with a VCC node between the power supply resistor and one end of the capacitor; the other end of the capacitor is connected to a node between the source electrode of the power switch and the inductance charging/discharging current detection resistor and is used as a filter capacitor of the constant current source load;

a controller integrated circuit providing overcurrent protection for the power switch based on an inductive charge/discharge current detection signal from a power conversion stage; and, on the basis of shielding the inductance charging current detection signal from the inductance charging/discharging current detection signal, determining the average output current of the constant current source load.

2. The driving apparatus as claimed in claim 1, wherein the controller integrated circuit is internally provided with a constant current error circuit, an overcurrent protection circuit and a driver, wherein,

the constant current error circuit shields the inductance charging/discharging current detection signal according to the driving signal output by the driver; and performing integral averaging on the inductor discharge current detection signal to generate an amplified error signal;

the overcurrent protection circuit receives the amplified error signal and the inductive charging/discharging current detection signal and generates a PWM signal;

and the input end of the driver receives the PWM signal, and the output end of the driver is connected with the grid electrode of the power switch.

3. The driving apparatus as claimed in claim 2, wherein the constant current error circuit comprises first and second NMOS transistors, an inverter, and an error amplifying circuit, wherein,

the drain electrode of the first NMOS tube is connected with one input end of the error amplification circuit, the source electrode of the first NMOS tube is connected with the reference ground of the controller integrated circuit, and the grid electrode of the first NMOS tube receives the driving signal output by the driver;

a drain electrode of the second NMOS tube receives the inductive charging/discharging current detection signal, a source electrode of the second NMOS tube is connected with the input end of the error amplification circuit, and a grid electrode of the second NMOS tube receives the driving signal through the phase inverter;

and the other input end of the error amplifying circuit is connected with a first reference voltage, and the output end of the error amplifying circuit generates an amplified error signal.

4. The driving apparatus of claim 2, wherein the constant current error circuit includes a screening resistor, an NMOS transistor, and an error amplifying circuit, wherein,

one end of the shielding resistor is connected with the inductance charging/discharging current detection signal, and the other end of the shielding resistor is connected to a node between the drain electrode of the NMOS tube and one input end of the error amplification circuit;

the source electrode of the NMOS tube is connected with the reference ground of the controller integrated circuit, and the grid electrode of the NMOS tube receives the driving signal output by the driver;

5. The driving apparatus as claimed in claim 4, wherein the resistance of the shielding resistor is more than 100 times smaller than the resistance of the integrating resistor in the error amplifying circuit and more than 100 times larger than the resistance of the inductive charge/discharge current detecting resistor.

6. The driving apparatus according to claim 3 or 4, wherein the overcurrent protection circuit includes a peak comparator, a current limit comparator, a valley comparator, an AND gate circuit, and a flip-flop,

a peak comparator, one input end of which receives the amplified error signal, the other input end of which receives the inductive charging/discharging current detection signal, and the output end of which is connected with one input end of the AND gate circuit;

a current-limiting comparator, one input end of which receives the inductance charging/discharging current detection signal, the other input end of which is connected with a second reference voltage, and the output end of which is connected with the other input end of the AND circuit;

a valley comparator, one input end of which receives the inductance charging/discharging current detection signal, the other input end of which is connected with a third reference voltage, and the output end of which is connected with the reset end of the trigger;

and the setting end of the trigger is connected with the output end of the AND gate circuit, and the output end of the trigger generates the PWM signal.

7. The driving apparatus as recited in claim 6 wherein said third reference voltage is at or near zero volts.

8. The driving apparatus as claimed in claim 6, wherein the second reference voltage is 3 times or more than 3 times the first reference voltage.

9. A lighting fixture, comprising the driving apparatus of any one of claims 1 to 8 and an LED load.